1. Field of the Invention
The present invention relates to an apparatus for controlling the silver ion concentration in the precipitation of a silver halide emulsion. More particularly, the invention relates to a linearizing circuit in a control loop in the apparatus. 2. Description of the Prior Art
In the precipitation stage of a silver halide emulsion it is crucial that accurate control of the flow rate of the silver salt and halide salt solutions be maintained. Accurate control of the rate of addition of the solutions is required during precipitation especially at the early stages, as variations in the rates of delivery may have adverse effects upon the number of nuclei formed and therefore the final grain size of the emulsion produced. Control systems utilizing a programmer for programming the rates of addition of an aqueous silver salt and an aqueous halide salt solution in the precipitation of a silver halide emulsion, a sensor for sensing and producing a signal representative of the silver ion concentration in the precipitation vessel, a set point generator for producing a set point signal to produce an error signal for use in correcting an unbalance of silver and halide in the emulsion are known in the art. It is further known to linearize the output of a sensor measuring fluid flow in a conduit. However, nothing in the prior art relating to control loop circuits and sensors immersed in a silver halide precipitation vessel solves the problem of non linear sensor output due to the non linear characteristics of the measured variable silver ion concentration in the precipitation process which results in unwanted over or under corrections by the controller. What is needed is improved apparatus for controlling the ratio of silver ions to halide ions in the emulsion in which such a non linearity is taken into consideration.